Iranian protesters set fire to the Saudi Embassy in Tehran during a demonstration against the execution of prominent Shiite Muslim cleric Nimr al-Nimr by Saudi authorities on Jan. 2, 2016.

Iranian protesters set fire to the Saudi Embassy in Tehran during a demonstration against the execution of prominent Shiite Muslim cleric Nimr al-Nimr by Saudi authorities on Jan. 2, 2016.

(Mohammadreza Nadimi, AFP/Getty Images)

Liz SlyWashington Post

Saudi Arabia severed diplomatic relations with Iran on Sunday, escalating the regional crisis that erupted after the execution of a Shiite cleric triggered outrage among Shiites across the Middle East and beyond.

Saudi Foreign Minister Adel al-Jubeir told reporters in Riyadh that the Iranian ambassador to Saudi Arabia had been given 48 hours to leave the country, citing concerns that Tehran's Shiite government was undermining the security of the mostly Sunni kingdom.

Saudi diplomats had already departed Iran after angry mobs trashed and burned the Saudi Embassy in Tehran overnight Saturday, in retaliation for the execution of Sheik Nimr Baqr al-Nimr earlier in the day.

The rift sets the region's two biggest powerhouses on a collision course at a critical time for U.S. diplomacy aimed at bringing peace to the Middle East, and it raised the specter of worsening violence in countries where they back rival factions, such as Yemen and Syria.

Despite their countless international feuds, it was the first time since a two-year rupture in 1988-1990 that diplomatic relations between Iran and Saudi Arabia had formally been severed, according to Abdullah al-Shamri, a Saudi analyst and former diplomat.

Nimr was among 47 people put to death on the biggest single day of executions in Saudi Arabia since 1980. He was one of only four Shiite Muslims in the group and was by far the best known. Most of the others were Sunnis accused of carrying out a spate of attacks linked to the Sunni al-Qaeda organization over a decade ago.

The cleric's role as a leader in the anti-government protests that swept the Shiite eastern regions of Saudi Arabia nearly five years ago ensured that his death sentence would be carried out and that there would be an enraged response from Shiites across the region.

In tough comments Sunday, Iran's supreme leader, Ayatollah Ali Khamenei, predicted "divine retribution" for Nimr's executioners, saying that the execution "will cause serious troubles for the politicians of this [Saudi] regime in a very short time."

"The hands of divine vengeance will surely snatch - by their necks - those cruel individuals who took his life," he said in comments posted on his website. A photo montage alongside the statement showed a split image of an Islamic State fighter preparing to carry out a beheading and a Saudi executioner, asking the question "Any difference?"

Saudi Arabia responded with an angry statement pointing out that Iran is often accused by the international community of supporting terrorism and of executing large numbers of people.

Iran "is the last regime in the world that could accuse others of supporting terrorism," said a Foreign Ministry statement reported by the official Saudi news agency.

Iran carried out 694 executions in the first half of last year, according to an Amnesty International statement in July. Saudi Arabia, whose population is about a third the size of Iran's, carried out 157 in all of 2015, according to Amnesty and media reports.

Beyond the invocations of divine justice, however, Iran made no specific threats of retaliation, and Iranian leaders ordered a halt to attacks on Saudi diplomatic facilities after the assaults on the Saudi Embassy in Tehran and the Saudi Consulate in Mashhad late Saturday.

Police officers were deployed to protect the charred remains of the Saudi Embassy, which had been ransacked and set ablaze by an angry crowd. Protesters who tried to gather nearby were dispersed by water cannons, according to photos posted on social media. The Iranian government announced that it had arrested 40 people in connection with the attack on the embassy.

"In no way is this justifiable," President Hassan Rouhani said on his Twitter account. "All Iranian officials are fully committed to confront these illegal acts."

In Lebanon, Hasan Nasrallah, leader of the Shiite Hezbollah movement, which is closely aligned with Iran, urged his followers not to rise to the bait of what he cast as sectarian provocation on the part of Saudi Arabia.

"The House of Saud wants to stir Sunni-Shiite sectarian strife everywhere, and our people must be aware of this and must not turn the issue into a Sunni-Shiite conflict," he said. To do so would be "an act of betrayal of the blood of Sheik al-Nimr, and it serves the purpose of his killers."

But the furor went deeper than the execution of a single cleric, striking at the heart of the Saudi-Iranian rivalry that has fueled, though not caused, much of the conflict engulfing the region.

Encouraged by Washington and by the regional realignment underway in the wake of the deal over Iran's nuclear program, the two rivals had been tentatively exploring closer ties, and it is unclear whether Saudi Arabia intended such a rupture when it carried out the death penalty against Nimr.

The execution is in keeping with the newly aggressive stance adopted by King Salman, who has worn the crown for a little less than a year since the death of his half-brother, Abdullah, and it sent a powerful message that Saudi Arabia is intent on standing up to its regional rival, said Theodore Karasik of Gulf State Analytics, a consulting group.

"The Saudis hope to demonstrate that they are on the offensive in terms of the Sunni-Shiite divide, and they have just upped the ante on that significantly," he said.

Saudi analysts question, however, whether the authorities in Riyadh intended or even foresaw the uproar that would ensue.

The different branches of Saudi Arabia's government do not always coordinate, and it is unclear whether the Foreign Ministry, which has been taking steps to mend relations with Iran, would have been informed, said al-Shamri, the Saudi analyst.

A new Saudi ambassador to Iraq, whose Shiite-led government has also responded with outrage to the execution, was dispatched only days before the execution. Riyadh had been preparing to send a new ambassador to Tehran, after the previous envoy was withdrawn amid criticisms of a kiss, widely broadcast on social media, that he shared with Iranian politician Ali Akbar Hashemi Rafsanjani.

"That tells me there was no timing. It was not planned," al-Shamri said, pointing out that Nimr had been sentenced in 2014 and that the government had announced the plan for the mass execution in November. "Bureaucracy in Saudi Arabia is very slow."

The Saudi government may simply have been seeking to strike a sectarian balance in carrying out the death penalty against so many people, said Toby Matthiesen, an expert on Saudi Arabia at Britain's Oxford University. Some prominent figures were included in the group of 43 Sunnis put to death, and Saudi Arabia has to tread as carefully with its majority Sunni constituency as it does with the minority Shiites.

Maybe, he said, "they threw in a few Shia amongst the Sunni militants that were executed to say, 'We are evenhanded, we execute both Sunni and Shia.'"